Abrasive articles



Patented Apr. 1, 1947 airman s'rAr s PATENT orrics ABRASIVE ARTICLES Charles E. Drake, Bloomfield, N. .L, assignor to United States Rubber Company, New York, N. Y., a corporation of New Jersey No Drawing. Application June 30, 1545, Serial No. 602,873

8 Claims. AC1. 51*299) bonded by an irreversible or non-thermoplastic bond, for example, hard vulcanized rubber, or synthetic resin of the phenol-formaldehyde or similar type, are well known. In the hard-rubber type bond, the rubber is mixed with about one-half its weight of sulfur, the abrasive grains mixed in, and the material vulcanized to a hard non-resilient grinding wheel or other kind of abrasive article.

According to the present invention, a hardrubber type bonded. abrasive article is produced that has appreciable flexibility and resilience, yet

approaches the strength of ebonite. Although a soft rubber compound may be loaded with fillers so as to have almost any degree of hardness, such highly loaded soft-vulcanized rubber compounds, if used as a bonding medium for abrasive grains, will be found very poor in mechanical strength, and if less filler is used, the vulcanized compound will be too soft for many uses, being unable to hold the abrasive grains in place flrmly enough to do the work expected of them.

In carrying out the, present invention, the abrasive grains are bonded with a vulcanized composition containing hard rubber and a. synthetic rubber-like material which willcure ir- 2 flexible hard-rubber bond for the abrasive grains is formed. U. S. patent to Patrick 1,8 0, 91

reversibly to a state resembling soft vulcanized rubber but which will not cure to a hard state comparable to that of hard rubber. Examples of such synthetic rubber-like materials that may be mixed with the rubber and sulphur, and vulcanized to give a resilient and flexible hardrubber type of abrasive article are certain of the so-called organic polysulphide polymer plastics. These synthetic rubber-like materials are obtainable commercially in an intermediate or partially polymerized and plastic state resembling unvulcanized rubber, and may be cured in a known manner to an elastic state resembling soft vulcanized rubber, but not to a hard state comparable to hard rubber. When abrasive grains are incorporated in a blend of these partially V polymerized materials with a hard rubber mix and the mass cured or vulcanized, a resilient and describes the reaction between alkali polysulphides and oleflne compounds, particularly the dihalides, to produce the well known oleflne polysulphide plastics, for example, the reaction products of alkali polysulphides and ethylene dichloride to produce ethylene polysulphide polymers. Such olefine polysulphide plastics are substantially polymers of the structural unit rodiethyl ether and dichlorodiethyl formal. to"

give oxydiethylene polysulphide polymers and methylene dioxydiethylene polysulphide polymers, respectively. In these compounds, the space between the adjacent carbon atoms in the above referred structural unit is opened up and an intervening ether linkage structure is employed, giving polymers of the structural unit where represents two carbon atoms separated by and joined to an intervening structure characterized by an ether linkage. The above polymers or the structural units will be termed herein as organic polysulphide polymer plastics." They are known commercially under the trade name Thiokols. The polymers of substantially the structural units [ii-t "*1 for example, ethylene polysulphide polymers having four to six sulphur atoms per repeating unit, viz. polymers of the repeating structural and . 3 unit [C2H4S4 to 6-], and the polymers of substantially the structural unit I I Jll...i%-Snor-] where the repeating structural unit and methylene dioxydiethylene polysulphide polymers having two to six sulphuratoms per repeating unit, viz., polymers of the repeating structural unit may be cured or vulcanized in a known manner,

generally by heating in the presence of 10 to 20 parts of zinc oxide per hundred parts of the Thiokol, to a state resembling soft vulcanized rubber but will not cure to a state comparable to hard rubber.

The term rubber as used herein, as in reference to soft vulcanized rubber and hard rubber, means natural rubber. It is well known that there are vast difierences in the physical properties of soft vulcanized rubber, which contains up to 10 parts of combined sulphur per 100 parts of rubber, and hard rubber which contains 30 to 4'7 parts of combined sulphur per 100 parts of rubber. The terms "soft vulcanized rubber and hard rubber are well understood in the art and the properties that distinguish one from the other are so well known that no further definition-or distinction need bemade than by use of these terms. As illustrative of the great difference in properties of the two materials, the modulus of rigidity of soft vulcanized rubber is of the order of 20 to 100 lbs. per sq. in., while the modulus of rigidity of hard rubber or ebonite is of the order of 100,000'to 200,000 lbs. per sq. in. Theelongation at break of soft vulcanized rubber is several hundred percent, while the elongation at break of hard rubber is.generally less than fifteen percent. Copolymers of a major proportion of butadiene-l,3 and a minor proportion of a monovinyl compound such as styrene or acrylic nitrile will cure on heating with twenty to forty or more parts of sulphur per. one hundred parts of the copolymer to a condition or 7 state in which their physical properties are com..

parable to those of hard rubber as described above. sulphide polymer plastics specified above will vulcanize only to a state or condition in which their physical properties resemble those of soft rubber, as described above, but will not cure to vulcanize to a state in which their properties are comparable to those of hard rubber.

The preferred proportions of rubber and organic polysulphide polymer plastic in the bond composition are within the range 1:5 to :1 parts by weight. With such proportions, bonded abra sive articles with widely varying grinding qualities, flexibility and hardness maybe made.

Preferably, the rubber and sulphur are first mixed on a rnilland then the partially polymerized rubberlike material, i. e., the organic poly- On the other hand, the organic poly-' given quantity of abrasive grains, such as aluminum oxide, silicon carbide, or any of the regularly known abrasives. After mixing the blended intermediate polymerized rubberlike material and hard rubber stock with the abrasive, the resulting mass may be formed into the desired shape of the article and cured. In making grinding wheels, the mix may be sheeted out to the prescribed thickness and, before or after cutting or dieing to shape, heat-cured, as in a press, for example, at: 50 pounds steam pressure for upwards of three hours.

As illustrative of the invention, an example of a typical formula for the bond composition is as follows, the amounts of ingredients indicated being parts by weight: 100 parts of smoked sheet natural rubber, 50 parts of sulphur, 100 parts of Thiokol, and 20 parts of zinc oxide, together with such amounts of anti-oxidants, accelerators, etc., as are desired. For example, four parts of diphenyl guanidine may be added to the above formula as an accelerator. Another formulation for bond compositions is 100 parts of smoked sheet natural rubber, 50 parts of sulphur, 80 parts of Thiokol, and 8 parts of zinc oxide per 100 parts of Thiokol in the compound. The Thiokol in the formulas may be any of the commercial organic polysulphide polymer plastics which can be cured to a state resembling soft vulcanized rubber but not to a state comparable 5 to hard rubber. Twenty parts by weight of the above bond compounds were mixed with 80 parts by weight of abrasive grains, and the masses sheeted and formed into grinding wheels which were press-cured. The cured compositions of the present invention are not limited to bonding abrasives. The natural rubber and butyl rubber with the vulcanizing ingredients may be sheeted or molded, and cured or vulcanized with or without contact or attachment to some other mate- 45 rial, such as fabric or metal, to give hard-rubber type vulcanizates where additional flexibility and resilience is desired. i

In view of the many changes and modifications the group consisting of polymers of one of the repeated structural units E-CaHs-Si to 6-],

2. An abrasive article comprising abrasive grains and a bond containing the vulcanization product of a mixture of rubber, sulphur in amount to vulcanize said rubber tohard rubber, and a organic polysulphide polymer plastic selected from the group consisting of ethylene polysulphide polymers having four to six sulphur atoms per repeating unit, oxydiethylene polysulphide polymers having two to six sulphur atoms per lepeating unit, and methylene dioxydiethylene polysulting blend may then be mill-mixed with a the proportions of rubber and, the organic polysulphide polymer plastic being within the range 1:5 to 5: 1 parts by weight.

4. An abrasive article comprising [abrasive grains and a bond. containing'the vulcanization product of a mixture of rubber, sulphur in amount to vulcanize said rubber to hard rubber, and an or anic polysulphide polymer plastic selected from the group consisting of ethylene polysulphide polymers having four to six sulphur atoms per repeating unit, oxydiethylene polysulphide polymers having two to six sulphur atoms per repeating unit, and methylene dioxydiethylene polysulphide polymers having two to six sulphur atoms per repeating unit the proportions of rubber and the organic polysulphide polymer plastic being within the range 1:5 to 5:1 parts by weight.

5. An abrasive article comprising abrasive grains and a bond containing the vulcanization roduct of a mixture of rubber, sulphur in amount to vulcanize said rubber to hard rubber, and an organic polysulphide polymer plastic of the repeating structural unit [-CzI-I4OC2H4-Sz to e-] 6. An abrasive article comprising abrasive 6 grains and a bond containing the vulcanization product oi a mixture of rubber, sulphur in amount to vulcanize said rubber to hard rubber, and an organic polysulphide polymer plastic reaction product of an alkali polysulphide and dichlorodiethyl ether.

7. An abrasive article comprising abrasive grains and a bond containing the vulcanization product of a mixture of rubber, sulphur in amount to vulcanize said rubber to hard rubber, and an organic polysulphide polymer plastic oi. the repeating structural unit the proportions of rubber and the organic polysulphide polymer plastic being within the range 1 :5 to 5: 1 parts by weight. I

8; An abrasive article comprising abrasive grains and a bond containing the vulcanization product of a mixture of rubber, sulphur in amount to vulcanize said rubber to hard rubber. and an organic polysulphide polymer plastic reaction product of an alkali polysulphide and dichlorodiethyl ether, the proportions of rubber and the organic polysulphide polymer plastic being within the range 1:5 to 5: 1 parts by weight.

CHARLES E. DRAKE.

REFERENCES CITED The following references are of record in the file of this patent;

UNITED STATES PATENTS Number Name Date 1,890,231 Patrick et al Dec. 6, 1932 2,040,698 Lewis et a1 May 12, 1936 2,384,683 Kistler Sept. 11, 1945, 

